1. Field of the Invention
The present invention relates to parking devices for disk drives; more particularly, to devices which position and retain the head(s) of a disk drive over a selected portion of a hard (or fixed) disk when the disk drive is not in use.
2. Description of the Related Art
Conventional hard disk drives often incorporate a device for parking the head(s) of the drive. As used in this patent, the terms "park" and "parking" refer to maintaining the position of the head(s) over a selected portion (usually a "landing zone" at the inside or outside diameter) of the disk (or disks) by latching the actuator which supports the head(s). Many parking devices park the head(s) by physically engaging (latching) the actuator, and the terms "latched" and "unlatched" respectively refer to the engagement and disengagement of the parking device and the actuator.
In conventional disk drives, a head "flys" over the surface of a disk, riding on the stream of air created by the rotation of the disk. When the disk stops rotating, for example, when power is turned off, the head lands on the disk. If the head lands on a portion of the disk which is used to store data, there is a possibility that the disk, and thus the data stored on the disk, will be damaged. In addition, physical shocks experienced during shipping or other non-operational movements of a disk drive may cause the head to "slap" against the disk, Possibly causing a loss of data if the head slaps against a data-carrying portion of the disk. Parking the head assures that the head will land on the landing zone--i.e., a non-data storage portion of the disk--and will be held in a position over the landing zone during the power down period.
Various types of parking (or latching) devices have been used to look the actuator arm of a voice coil in a selected position when the disk drive is not operating. Many parking devices utilize a spring biased pivoting latch arm which holds the actuator in a parked position under the force of the spring when the disk drive is not in use and an electromagnet to release the latch during operation of the drive.
Air activated parking devices rely on the air flow generated by the rotating disks to release a spring biased latch arm. Other parking devices use a solenoid to release a latch arm.
In parking devices which utilize an electromagnet to attract a clapper plate, the clapper is at its farthest distance from the electromagnet when the head is parked, and the capture force necessary to release the latch is greatest when the head is parked. Accordingly, to ensure reliable latch release, the electromagnet must create a strong enough capture force to overcome the biasing force when the clapper plate is at its farthest distance from the electromagnet and the effect of the electromagnet on the clapper is at a minimum. Further, the spring or other means used to bias the latch arm to the latched position must provide a large enough biasing force to overcome any residual magnetism in the clapper, thereby increasing the required capture force.
To create a large enough force to release a latch arm, a solenoid must be relatively large. And, as with an electromagnet, the solenoid must develop the largest force at the beginning of its stroke--i.e., when the solenoid is least able to generate force. Air activated parking devices may pose the problem of interference with the air flow necessary for the heads to fly properly. Additionally, the air flow in a disk drive is only sufficient to create a relatively small release force, creating reliability problems for latch release. The lack of release force also means that the biasing force must be relatively small, thereby decreasing reliability of parking (latching).
Purely magnetic parking devices park the actuator by the attraction of and direct contact between a magnetically permeable portion of the actuator and a magnet. The primary drawback of a magnetic latch of this type is that during operation of the disk drive the rotational movement of the actuator is adversely affected by the attraction of the magnetically permeable portion of the actuator and the magnet, thereby creating problems with the track following and seek functions. Further, an extremely large force is required to release the actuator from the magnet.